In regards to the black tank flush line, any water past the anti-siphon valve will drain into the tank, thus clearing that section of line. From the UDC fitting up to the anti-siphon, it may or may not drain out on it's own. Originally, my UDC fitting for it did not have a check valve, just a hollow plastic tube, something like a flow restrictor, nothing more. I've since replaced the fitting (it broke) with a city water connection with check valve. Pressing the valve pin open, I drained about a 1/2 cup of water from the line.
I also remove the battery and bring it home. I'll give it a charge a couple of times over the winter to keep it happy. The use of dryer sheets may work for some mice. The ones around me used it for toilet paper. One of the drudgery chores is to go around the frame of the rig, sealing up any opening you can to keep the little buggers out. But it may appear that Mickey has gone over to the Star Trek set and borrowed a transporter beam to get inside.
Don't forget to inflate your tires to the max. cold pressure and put covers on them. Not a bad thing to park the rig with the tires up on a piece of wood, rather than in the dirt over the winter. Remove anything in the storage areas that might freeze and burst, too. Remove the TV's and any other valuables and put a sign on the rig that you've removed all valuables. Might help keep burglars from busting in, might not, depending on how big of a hurry they're in.
